Generally, golf balls have been classified as solid balls or wound balls. Solid balls are generally comprised of a solid polymeric core and a cover. These balls are generally easy to manufacture, but are regarded as having limited playing characteristics. Wound balls are comprised of a solid or liquid filled center surrounded by tensioned elastomeric material and a cover. Wound balls generally have a good playing characteristics, but are more difficult to manufacture than solid balls.
The prior art is comprised of various golf balls that have been designed to provide optimal playing characteristics. These characteristics are generally the initial velocity and spin of the golf ball, which can be optimized for various players. For instance, certain players prefer to play a ball that has a high spin rate for playability. Other players prefer to play a ball that has a low spin rate to maximize distance. However, these balls tend to be hard feeling and difficult to control around the greens. Therefore, attempts to create a golf ball that couples the production ease of a solid ball with the beneficial playing characteristics of a wound ball, have been numerous.
A Japanese Publication No. 10127819 is directed towards a method for constructing a solid golf ball that provides a “soft” ball-hitting touch. The golf ball consists of a solid core of a three layer structure comprising an internal layer, an intermediate layer, and a cover layer, and a cover over the solid core. The internal layer of the three-layer structure is set to a JIS-C hardness of 40-90, the intermediate layer is made up of a thermoplastic resin composition to be set to a JIS-C hardness of 50-80, and the cover layer is set to a JIS-C hardness of 65 or more.
Another reference, U.S. Pat. No. 5,184,828 discloses a dual core golf ball whose core has a maximum hardness at the surface of the inner core and then increases in hardness from the surface of the inner core to the center of the inner core and from the surface of the inner core through the body of the outer core. Specific hardness ranges for each location are specified but the patent does not address the use of soft elastomeric film between layers.
Similarly, Japanese Patent Application No. 8-322964A of Kasco Corporation discloses a dual core ball whose core has an increasing hardness gradient, requiring that the inner surface of the outer core be harder than the remainder of the outer core.
The prior art additionally discloses a number of methods for the manufacture of golf balls employing a soft elastomeric film (such as a latex dip) on wound constructions. U.S. Pat. No. 5,733,428 discloses the use of latex dips within the body of a wound core to produce multilayer wound cores. The prior art also discloses the concept of a coating between the core and the outer cover of the ball; the coatings were comprised of fully-cured epoxy or other adhesive material to help increase core to cover adhesion.
However, none of these patents disclose or even suggest a nonwound, dual, multicore or liquid-center ball having the materials and material property requirements as disclosed herein, specifically the use of a soft, intermediate layer between the inner sphere and subsequent mantle layers, to provide the improved balls of the present invention. The softer, rubber interlayer can serve as a cushioning interface to improve the overall softness of the ball, as well as the fracture durability.